Very basic image proxy

server.js

'use strict';

const express = require('express');
const crypto = require('crypto');
const got = require('got');

const signingKey = 'some sort of key here';

const proxyHeaders = [
  'content-length',
  'content-type',
  'etag',
  'expires',
  'last-modified',
  'vary'
];

var app = express()
app.disable('x-powered-by');

app.get('/:imageSignature/:imageUrl', function (req, res, next) {
  const imageSignature = req.params.imageSignature;
  const imageUrl = req.params.imageUrl;

  // compare signature
  const hmac = crypto.createHmac('sha256', signingKey);
  hmac.update(imageUrl, 'utf8');
  var expectedSignature = hmac.digest('hex');

  console.log(req.params)
  console.log('expectedSignature', expectedSignature);

  if(expectedSignature !== imageSignature) {
    var err = new Error('Requested signature does not match');
    err.status = 400;
    return next(err);
  }

  console.log('Request headers', req.headers);

  var headers = {
    'Accept': req.headers.accept || 'image/*',
    'User-Agent': req.headers['user-agent'],
  };

  return got.get(imageUrl, { headers: headers })
    .then(function(imageResponse) {
      console.log('response headers', imageResponse.headers)
      proxyHeaders.forEach(function(header) {
        var headerValue = imageResponse.headers[header];
        if(headerValue) {
          res.setHeader(header, headerValue);
          console.log('set header', header, headerValue)
        }
      })
      res.status(imageResponse.statusCode)
        .send(imageResponse.body)
    })
    .catch(function(err) {
      err.status = 400;
      return next(err);
    })
})

app.listen(3000)